Which statement best describes chlorine dioxide in disinfection?

• A. It is an effective disinfectant and a strong oxidizer, but can be hazardous to handle and requires monitoring of residuals.
• B. It is a weak disinfectant that is safe to handle and requires no residual monitoring.
• C. It is only effective in high pH conditions and has no residual risk.
• D. It cannot be used for disinfection.

Answer: (A)

Chlorine dioxide acts as a disinfectant through oxidation, inactivating a wide range of microorganisms. It’s a strong oxidizer used in water treatment because it can kill bacteria and viruses effectively and tends to form fewer chlorinated disinfection byproducts than traditional chlorine. But handling chlorine dioxide requires care: it is toxic and an oxidizer, so operators must generate and manage it on-site with proper safety controls and ventilation. Because maintaining an appropriate residual is key to continued disinfection downstream, residual monitoring is essential to ensure the water remains adequately disinfected and to manage any regulated byproducts like chlorite and chlorate. This makes the statement accurate: it describes both its effectiveness and its safety and monitoring needs. It isn’t a weak disinfectant, isn’t safe to handle without precautions, isn’t limited to high pH, and it is indeed used for disinfection.